The present invention relates to an armature with a closure that can be displaced along an ascending spindle in a housing, the spindle being connected by means of a spindle sleeve accommodated in the valve housing and of a transition bushing fastened to the spindle sleeve with an electric-motor adjusting mechanism and a stroke-limiting nut being screwed onto the spindle.
Armatures of this type must be remotely operated with an electric-motor adjusting mechanism. Whereas the armature necessitates a translational force (introduction and extraction of a spindle) for its operation, the adjusting mechanism carries out a rotational motion. The torque is converted into an axial force by means of a spindle sleeve mounted in a ball bearings and of trapezoidal threading cut into the valve spindle. The motion of the spindle as it closes the armature is limited by a stroke-limiting nut screwed onto and secured on the valve spindle.
When a combination of armature and adjusting mechanism is of high significance from the aspect of safety, as in a nuclear power plant for example, various failure potentials must be reliably controlled. One potential failure is the breakdown of power controls, when the adjusting mechanism drives the stroke-limiting nut at a maximum torque that is higher than the flywheel effect on the spindle sleeve that results from the rotating masses. The height of the flywheel effect during startup into stroke limiting at a given adjustment mechanism is a function of the rigidity of the armature. The known system has a very high rigidity. The resulting initiating forces and moments can lead in many cases to destruction of the armature and adjusting mechanism.